1. Field of the Invention
The present invention relates to a toroidal-type infinitely variable transmission used for vehicles, such as automobiles.
2. Description of the Prior Art
A toroidal-type infinitely variable transmission for a fore-engine rear wheel drive car is disclosed, for example, in U.S. Pat. No. 3,299,744.
In this prior art transmission, an input shaft connected to an engine is rotatably supported by a housing through bearings, and an input disk and an output disk are rotatably disposed on the input shaft in successive order. Power rollers are provided between the input disk and the output disk and are rollably in contact therewith. A rotation force of the input shaft is transmitted to the input disk through a cam and sprag device. A Belleville washer is interposed between the input shaft and a shaft bearing provided on a stationary portion which supports the input shaft. The Belleville washer presses the input disk towards the output disk.
However, in the toroidal-type infinitely variable transmission mentioned above, since the input shaft is supported by the shaft bearing which is secured to the housing, in transition from a condition in which the input disk is pressed by the Belleville washer through the input shaft to a condition in which the input disk is pressed by a cam, although the input shaft moves backwardly against a biasing force of the Belleville washer, the backward movement of the input shaft is performed slowly due to a large slide resistance between the input shaft and the shaft bearing. As a result, the action of a pressing force of the cam on the input disk is delayed, and an increase in thrust cam not follow an increase in input torque. Thus, a serious problem is involved in that in the worst case, a slip is caused between the input disk and the power rollers, causing the power transmission function to be lost.
Another toroidal-type infinitely variable transmission for fore-engine front wheel drive cars and two wheelers is generally structured as shown in FIG. 3 because it is impossible to retain a large space for accommodating the transmission.
Specifically, an input shaft 1 whose right end is connected to a rotation drive, such as an engine, through a clutch is rotatably supported at opposite ends by bearings 3 and 4 which are secured to a housing 2. An output disk 5 and an input disk 6 are rotatably disposed with a predetermined interval therebetween on the input shaft 1 from the side of the rotation drive in this order. Power rollers 7 are rollably and tiltably disposed between both of the disks 5 and 6. Further, a pressing mechanism 8 is disposed at one side of the input disk 6 opposite to the output disk 5 so that no slip is caused between the input disk 6 and the power rollers 7 and between the output disk 5 and the power rollers 7.
The pressing mechanism 8 is comprised of a loading nut 9 secured to the input shaft 1, a loading cam 11 opposing the loading nut 9 through a pressure adjusting Belleville washer 10 and serration coupled to the input shaft 1, and a roller 12 interposed between the loading cam 11 and the input disk 6.
During a period in which the input torque transmitted to the input shaft 1 is small, the input disk 6 is pressed against the output disk 5 by the spring force of the pressure adjusting Belleville washer 10, and a predetermined pressing force is exerted between the input disk 6 and the power rollers 7 and between the output disk 5 and the power rollers 7 so that a reduction in the power transmission efficiency due to the slip among these elements is prevented. From this condition, when the input torque is increased and a thrust greater than the spring force of the pressure adjusting Belleville washer 10 is required, the roller 12 rides on cam surfaces formed on opposing surfaces of the input disk 6 and the loading cam 11. As a result, the loading cam 11 moves the serration portion to the left against the pressure adjusting Belleville washer 10 so that the loading cam 11 directly contacts the loading nut 9 to push it to the left. This pressing force is received by the bearing 4 through the input shaft 1, and consequently, a pressing force corresponding to the input torque is exerted to a power transmission portion between the input disk 6 and the power rollers 7.
However, in the prior art toroidal-type infinitely variable transmission described above, since the loading cam is serration coupled with the input shaft, a large frictional force is created against the axial movement of the loading cam. In particular, in a light load transient condition in which a power transmitting condition by the spring force of the pressure adjusting Belleville washer is changed to a power transmitting condition by a cam force by the loading nut, loading cam, and rollers, when the frictional force in the serration coupling is large, an increase in the thrust can not follow an increase in the input torque, and in the worst case, a slip is caused between the input disk and the power rollers resulting in the lost of the power transmission function. This fatal problem has not been solved in the prior art toroidal-type infinitely variable transmission.
In order to solve this unsolved problem, it may be considered to set the spring force of the pressure adjusting Belleville washer at a high level. However, in this case, a frictional force at the bearing receiving the axial force of the input shaft is increased, and this, in turn, lowers the power transmission efficiency and causes a reduction in a service life of the bearing. Thus, this approach is not preferable.